Shear bolt

[vezult]

So I recently got a PTO driven chipper, and promptly broke a shear bolt on the PTO. Unfortunately, I don't have much experience with them. I looked at it prior to use, and my memory is that it was a grade 8.8 bolt. I did not measure the length. The head of the bolt disappeared when it sheared.

To be clear, this PTO has shear bolt built in, in front of the collar that fits onto a splined equipment shaft. This is *not* a shear bolt going through the middle of a smooth shaft. Docs for the implement don't cover the PTO driveline, and the doc that came with that is just generic.

I bought a replacement bolt at the hardware store, grade 8, same diameter, probably slightly longer. Is that OK, or am I doing something stupid? I'm kinda guessing.

Any guidance would be welcome.

 

[John Garner]

A Grade 8.8 is a metric specification,
and a Grade 8.8 fastener is significantly
weaker than a SAE Grade 8 fastener. I
don't remember off the top of my head if
a Grade 8.8 is closer to SAE Grade 5 or
SAE Grade 2, but you would probably be
wise to track down a few Grade 8.8
fasteners that fit.

 

[Russ from MN]

John is right, 8.8 is a metric bolt, similar to grade 5. But you want to get the correct bolt so it fits the hole properly. Any
good hardware store should have them.

 

[rustred]

dont even think of using a grade 8 bolt in there. shear bolts are like grade 2. so post a picture of what your working with . never use a
longer bolt either ... saftey first! bolts shear for a reason so u dont do other machine damage.

 

[showcrop]

In order to avoid major repairs I would start off with some softer grade bolts and work up. While there are some applications that call for a hard grade most are relatively soft.

 

[vezult]

(quoted from post at 21:28:22 06/05/21) A Grade 8.8 is a metric specification,
and a Grade 8.8 fastener is significantly
weaker than a SAE Grade 8 fastener. I
don't remember off the top of my head if
a Grade 8.8 is closer to SAE Grade 5 or
SAE Grade 2, but you would probably be
wise to track down a few Grade 8.8
fasteners that fit.

Thanks! I guess I assumed 8 ~= 8.8. This is the kind of knowledge I figured I was missing. I suspected I was probably doing something silly. Confirmed!

 

[SadFarmall]

If you have a manufacturer name on the PTO drive, you may be able to track down the correct shear bolt. The correct bolt is cheaper and, more importantly, safer than using the wrong ones.
Had issues with the shear bolt on an International 45 baler some years ago. It was a pain, but went to the trouble of buying correct replacements.
SadFarmall

 

[495man]

(quoted from post at 18:06:14 06/05/21) So I recently got a PTO driven chipper, and promptly broke a shear bolt on the PTO. Unfortunately, I don't have much experience with them. I looked at it prior to use, and my memory is that it was a grade 8.8 bolt. I did not measure the length. The head of the bolt disappeared when it sheared.

To be clear, this PTO has shear bolt built in, in front of the collar that fits onto a splined equipment shaft. This is *not* a shear bolt going through the middle of a smooth shaft. Docs for the implement don't cover the PTO driveline, and the doc that came with that is just generic.

I bought a replacement bolt at the hardware store, grade 8, same diameter, probably slightly longer. Is that OK, or am I doing something stupid? I'm kinda guessing.

Any guidance would be welcome.

Metric, 8.8 is the grade, measure the hole diameter and length, might be 6mm or 8mm, length is enough that you can get nut threaded on.

 

[DoubleO7]

What sadfarmall said.

Plus, length should be just long enough to install and one or two threads protruding from nut when tight.
And no threads between head and nut, especially in the area known as the shear plane(s).

 

[BarnyardEngineering]

Metric 8.8 is roughly the equivalent of Grade 5 SAE.

Longer is fine as long as the protruding bolt is not going to catch on something. A few seconds with a hacksaw will fix any "too long" problem.

 

[SVcummins]

My New Holland d1000 uses grade 8,8 shear bolts in the flywheel